1 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 14 Respiratory Monitoring in the Intensive Care Unit

2 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Learning Objectives After reading this chapter you will be able to:  Identify the methods, normal values, and significance of measuring the following lung volumes in the ICU: tidal volume, rapid-shallow breathing index, vital capacity, functional residual capacity

3 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Learning Objectives (cont’d)  Identify the methods, normal values, and significance of measuring the following airway pressures or related indices in the ICU: peak pressure, plateau pressure, compliance, airway resistance, mean airway pressure, maximum inspiratory pressure  List the definition, methods of detection, and methods of minimizing auto-PEEP

4 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Learning Objectives (cont’d)  Describe value of monitoring pressure, volume and flow waveforms, and pressure volume curves in mechanically ventilated patients  Describe methods and significance of measuring the fraction of inspired oxygen and exhaled carbon dioxide in the ICU  List the components of oxygen transport and their significance  List components of clinical evaluation of oxygenation and their significance

5 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Learning Objectives (cont’d)  Explain how these parameters can evaluate tissue oxygen delivery and use:  Oxygen delivery and availability  Oxygen consumption  Mixed venous oxygen tension  Venous saturation  Arterial to mixed venous oxygen content difference  Oxygen extraction ratio  Blood lactate

6 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Learning Objectives (cont’d)  Describe the value and limitations of pulse oximetry in monitoring oxygenation and oxygen delivery  Identify the techniques for monitoring tissue oxygenation and utilization

7 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Overview  Monitoring: repeated or continuous observations or measurements of the patient  Guide therapeutic interventions  Assess interventions  Alert clinicians to changes in patient’s condition

8 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Ventilatory Assessment  PaCO 2 : standard for assessing ventilation  Changes in metabolism, lung mechanics, ventilatory efficiency, equipment function may precede changes in blood gas  Ventilatory parameters monitored  Lung volumes and flows  Airway pressures  Fractional gas concentrations

9 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

10 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Lung Volumes and Flows  Why?  They affect gas exchange  They reflect changes in patient’s clinical status  They indicate response to therapy  They signal problems with patient/ventilator interface  Who?  Intubated and nonintubated patients

11 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Lung Volumes and Flows (cont’d)  What do we measure?  V T (5-8 ml/kg IBW) VT <5 ml/kg may indicate respiratory problem Pneumonia, COPD, CHF, ARDS, CNS depression Large VT in metabolic acidosis, sepsis, neurological injury  VT = V A + V D  V D = 25% to 40% of the VT V D >60% = need ventilatory support

12 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Lung Volumes and Flows (cont’d)  High VT ventilation with positive pressure: volutrauma  PEEP + smaller VT maintains FRC  Discrepancies between set/measured VT  Compressible volume of the circuit  Inspiratory and expiratory flow sensors  Pneumothorax  Leaks in the circuit or ETT

13 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Lung Volumes and Flows (cont’d)  Spontaneous breathing trial (SBT) failure:  VT <300 ml or <4 ml/kg  SpO 2 <85% to 90%  Blood pressure and heart rate change >20%  Respiratory rate >35/min  Change in mental status  Accessory muscle use  Diaphoresis

14 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.  Rapid shallow breathing index (RSBI)  RSBI = f (breaths/min)/VT (liters)  RSBI >105: prognostic of failure  V E = 5 to 6 L/min  V E > 10 L/min: weaning not likely successful Lung Volumes and Flows (cont’d)

15 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.  Vital capacity (VC)  65 to 75 ml/kg IBW  FVC <20 ml/kg preoperative: risk of pulmonary complications  VC 10 to 15 ml/kg needed for deep breathing and coughing  VC >10 to 15 ml/kg for successful weaning and extubation Lung Volumes and Flows (cont’d)

16 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.  Functional residual capacity (FRC)  FRC = 40 ml/kg IBW  PEEP and CPAP increase FRC  Beneficial in atelectasis and refractory hypoxemia as occurs with ARDS Lung Volumes and Flows (cont’d)

17 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures  Important to monitor airway pressures:  Need for mechanical ventilation and readiness for weaning  Determine site and cause of impedance to mechanical ventilation  Evaluate elastic recoil, compliance of thorax  Estimate amount of airway pressure transmitted to heart and major vessels  Assess respiratory muscle strength

18 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Peak pressure or PIP  Pressure required to overcome opposition to airflow in the lungs  Increased resistance Bronchospasm, airway secretions, mucus plugging  Decreased compliance (lung or chest wall)  Patient-ventilator interface problem

19 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

20 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Plateau pressure  Elastic recoil of lung and chest wall  Static pressure during period of no gas flow  Pressure required to maintain inflation

21 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

22 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Mean airway pressure (Paw)  Affected by CPAP, PEEP, inspiratory time (T I ), V T, PIP, and rate =  Paw = [½ (PIP – PEEP) × (inspiratory time/total cycle time)] + PEEP  Impacts oxygenation  Caution when Paw >20 cm H 2 O _ _ _

23 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Maximum inspiratory pressure (P Imax )  Influenced by: Respiratory muscle strength Patient effort/ventilatory drive Lung volume Phrenic nerve function Nutritional status Oxygenation/acid-base status  Normal P Imax : –80 to –100 cm H 2 O  P Imax > –30 cm H 2 O may be useful to predict successful weaning

24 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Auto-PEEP  Total PEEP – set PEEP  Reduction of auto-PEEP Bronchodilator therapy Decreased TI (allows more time for exhalation) Reduction of mechanical frequency Reduction of V E is the most effective

25 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Compliance  Dynamic compliance = {Corr VT – [(PIP – EEP) × CF]}/PIP – EEP  Static compliance = Corr V T - [(P plat - EEP) × CF]/P plat – EEP  Normal static compliance in patients receiving mechanical ventilation: 40 to 80 ml/cm H 2 O  Compliance <20 – 25 ml/cm H 2 O associated with failure to wean

26 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Airway Pressures (cont’d)  Airway resistance (Raw)  (Ra-w = PIP (cm H 2 O) – plateau pressure (cm H 2 O)/flow (L/sec)  Normal = 1 to 3 cm H 2 O/L/sec _ _

27 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Integrating Pressure, Flow, and Volume  Evaluating patient/ventilator interface  At the patient: use of accessory muscles, color, diaphoresis, heart rate, respiratory rate  At the airway: type, size, integrity, stability  At the ventilator circuit: leaks, temperature, condensate  At the ventilator settings and monitoring panel

28 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Integrating Pressure, Flow, and Volume (cont’d)  Monitoring pressure, flow, and volume  Graphic display screen  Scalar: a single parameter over time Pressure-time waveform Volume-time waveform Flow-time waveform  Loop: two parameters in a continuous tracing Pressure-volume loop Flow-volume loop

29 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Integrating Pressure, Flow, and Volume (cont’d)  Titrating PEEP and tidal volume with P/V  Static pressure-volume curve  Super syringe technique  Time consuming and cumbersome  Useful in acute lung injury  Lower inflection point + 2 cm H 2 O: minimal PEEP  Upper inflection point: overdistention

30 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

31 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Fractional Gas Concentrations  FIO 2  Exhaled CO 2  Capnometry and capnography  Affected by temperature changes, shivering, seizures, trauma, high carbohydrate infusion  Measure efficiency of ventilation  PETCO 2 : accurate estimate of PaCO 2  CPR effectiveness

32 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

33 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Dead Space-Tidal Volume Ratio  V D /V T  Anatomic dead space: 1 ml/kg IBW  Alveolar dead space  V D /V T = Pa CO 2 – PE- CO 2 /Pa CO 2  Normal: 25% to 40% _

34 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Evaluation of Oxygenation  Evaluation of oxygen transport  Oxygen consumption  Oxygen delivery (DO 2 )  Oxygen reserves  Oxygen content CaO 2 = (Hb × 1.34 × % saturation) + (PaO 2 × 0.003)  Cardiac output  Oxyhemoglobin dissociation curve

35 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

36 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

37 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Evaluation of Oxygenation (cont’d)  Monitoring adequacy of arterial oxygenation  Partial pressure of arterial oxygen Should be kept 60 to 80 mm Hg  Alveolar-arterial oxygen tension difference P(A-a)O 2  PaO 2 /FIO 2 ratio ALI: 200 to 300 ARDS: <200

38 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.  Monitoring adequacy of arterial oxygenation  Oxygen index = Paw × F IO 2 × 100/Pa O 2  OI >40: mortality >80% __ Evaluation of Oxygenation (cont’d)

39 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.  Intrapulmonary shunt  (QS/QT)  Increased in atelectasis, pneumonia, ARDS, pulmonary edema  Pulse oximetry will reveal low Sp O 2 with elevated F IO 2  Co-oximeter useful to determine Ca O 2.. Evaluation of Oxygenation (cont’d)

40 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation  Oxygen delivery (DO 2 )  Cardiac output × CaO 2 × 10*  Normal: 550 to 650 ml/min/m 2  Oxygen consumption (V O 2 )  Fick principle  Normal: 100 to 140 ml/min/m 2 *Change vol% to ml/L.

41 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

42 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation (cont’d)  Mixed venous oxygen tension Pv O 2  Normal: 38 to 42 mm Hg  Low: inadequate cardiac output, anemia, hypoxia  High: poor sampling technique, left-to-right shunt, septic shock, increased cardiac output, cyanide poisoning _

43 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

44 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation (cont’d)  Mixed venous oxygen saturation (Sv O 2 )  Fiberoptic reflectance oximetry  Decreased: suctioning, shivering, extubation, weaning, PPV _

45 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

46 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation (cont’d)  Arterial-mixed venous oxygen content difference, C(a – v) O 2 reflects:  Normal: 4 to 6 vol%  Increased: low cardiac output, increasing V O 2  Decreased: septic shock, increased cardiac output, anemia, left shift ODC _.

47 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation (cont’d)  Oxygen extraction ratio [C(a – v) O 2 /Ca O 2 ]  Normal: 25% to 30%  Increased: low cardiac output, increased VO 2, decreased CaO 2,  Decreased: high cardiac output, sepsis _.

48 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Monitoring Tissue Oxygenation (cont’d)  Blood lactate  Anaerobic metabolism = lactic acid production  Normal: <1.7 to 2.0 mM/L  >3.83 mM/L = 67% mortality  >8 mM/L = 90% mortality

49 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. Summary  Common ventilatory measurements  Lung volumes and flows  Airway pressures  Fractional gas concentrations  These measurements allow clinicians to determine the need for mechanical ventilation, monitor the patient, and determine the readiness for weaning